EP0555167B1 - Process for coating materials and products obtained by this process - Google Patents

Abstract

Coating process intended to bind adhesively binders which are plastic and elastic, either in fluidified form, as a result of the heat or of solvents, or in emulsified form, onto supports, especially of the granulate type, characterised in that it consists chiefly in pretreating the supports to be coated by making them hydrophobic and carry a positive electrical charge, so as to regularise their behaviour towards all the binders when hot or cold, and in all their forms, in giving them the ability to attract these binders, preferably in water, and in placing the said binders in contact with these hydrophobic supports with a view to their adhesive and homogeneous deposition on the said supports.

Description

The present invention relates to the field of coating of supports, in particular of aggregates, and relates to a generalized or universal coating process for plastic and elastic binders, mainly bituminous.

In various documents, including in particular the document FR-2608185, solutions have been proposed for cold coating with bitumen emulsions, the performance of which is comparable or superior to that of the hot coating technique, specifying that it these are bitumen-based emulsions, used in hot-coating, not softened by solvents.

These documents exploit the idea of using the facilities for manufacturing and stabilizing anionic emulsions - absent in cationic emulsions - to make them, under the guise of this stability, cationic emulsions. This stability is transmitted to cationic emulsions of this new type, which allows all cold coatings with the same formulas as the technique of hot coating currently makes possible. They have the ability - like direct cationic emulsions - to break on contact with mineral aggregates.

These methods avoid dust and lead to a simplification of the manufacturing apparatus. The heavy dusting necessary for hot coating is eliminated and the obligation to recompose the granular formulation, destroyed by the passage with a drying drum, can be avoided. The metering of bitumen can be carried out in the same precise manner as for hot coating by the mobile emulsion manufacturing plant described in particular in document FR-2 608 645, which can be incorporated in a cold coating station. Thus the bitumen arrives in the form of an emulsion, with a certain offset, on the aggregates to be coated, proportioned accordingly. In this case the percentage of water in the emulsion - vehicle of the dose of bitumen - does not matter, provided the transfer pumps are capable of absorbing the dose of bitumen, swollen in emulsion.

The present invention proposes to replace the cationic transformation of the anionic emulsion by a treatment of the mineral aggregates, in order to make them, once and for all hydrophobic. In this form they are adhesively coated with all forms of bituminous binders, including the universal anionic emulsion, described below.

Document US-A-3,761,296 discloses a process for the preparation of bituminous mixtures in which, on the one hand, an increase in the adhesiveness between the supports and the binders is obtained by the addition of a chromium compound and , on the other hand, a suppression of foaming by addition of a fatty acid.

The aforementioned document indicates that the two additives mentioned can be added either before, during or after the contacting of the supports with the binders.

This document makes no mention of the phenomenon of hydrophobation, nor of the creation of an electric charge at the level of the supports to be coated, before coating of the latter.

In addition, from document US Pat. No. 4,780,518, a process is known for treating absorbent supports in order to make them hydrophobic and lipophilic, as well as treated supports obtained by this process.

However, the process described applies specifically and exclusively to organic supports, and does not mention any possibility of application to mineral supports, a fortiori an application within the framework of the coating of supports of the aggregate type with a plastic binder and elastic such as bitumen.

In addition, this process uses large quantities of water for the impregnation of the supports with the active compounds, which subsequently requires a drying phase which is penalizing in energy expenditure.

Furthermore, no mention is made in this document of research or of obtaining an electric charge at the level of the treated supports, opposite to that of the binders to be fixed and causing mutual attraction between said supports and said binders.

Now, the subject of the present invention is a coating process, intended for adhesively fixing plastic and elastic binders, either in fluidized form, due to heat or solvents, or in emulsified form, on supports, in particular of the type aggregates, characterized in that it consists mainly in pretreating the supports to be coated, making them hydrophobic and carrying a positive electrical charge under the action of two specific chemicals, namely, on the one hand, an acid salt metallic and, on the other hand, an organic acid to long chain, so as to standardize their behavior with regard to all hot or cold binders, and in all their forms, to give them the ability to attract these binders, preferably with water, and to put said binders in contact with these hydrophobic supports, with a view to their adhesive and homogeneous deposition on said supports, this deposition being able to occur more or less long after said hydrophobic pretreatment.

The hydrophobicity of the supports to be coated can be obtained by the differentiated actions of iron sulfate FeSO ₄ 7H ₂ O and of an organic long chain acid, such as a fatty acid or a naphthenic acid.

After simultaneous or separate addition of the two specific chemicals on the supports to be hydrophobed, rapid cold drying of said products on the supports is advantageously carried out, requiring no addition of calories, or long drying manipulation and resulting in the acquisition by said supports of a positive electrical charge.

According to another characteristic of the invention, the binders used are hydrocarbon binders, in the form of the end of distillation of crude oils, cut or not with solvents and fluidized, if necessary, these binders being identical to those used for coating with classic hot or for cold coating on cut-backs.

Preferably, the hydrocarbon binders are used in the form of emulsions, the bitumen globules of which carry a negative electrical charge which break in contact with the hydrophobic supports by depositing the binder in a homogeneous and adhesive manner there, more or less rapidly. , depending on the degree of stability of said emulsions.

The stability of the emulsions is advantageously controlled by means of the levels of alkalis present in them, alone or in combination with proteins or other stabilizing agents, or alternatively rupture accelerating agents, such as, for example, MgSO ₄ , Na ₂ SO ₃ or petroleum solvents. The rates of accelerators and stabilizers, present in said emulsions, shorten or lengthen more or less the duration of this rupture, which can vary within large time ranges.

The different rupture accelerators can be, depending on their nature, either introduced into the coating emulsion together with the protein flour, in particular Na ₂ SO ₃ , or mixed, in the form of solutions, with the basic salt of trivalent chromium or with metallic acid salt, for MgSO ₄ for example, or with long chain organic acid (fatty acid), for petroleum solvents in particular, used to hydrophobize the supports to be coated.

The chromium or other metal salts, in particular of iron and the fatty acids or its aforementioned counterparts, are mixed in a homogeneous manner with the supports or aggregates to be treated, the latter then becoming capable of being validly and adhesively coated with a simple anionic emulsion which, overstabilized with an alkali, possibly with proteinaceous materials or with a mixture of the latter, makes their facets coated as described below, also promoting hydrophobicity.

In order to prevent any fines present from fluttering during the handling of the supports to be coated in the form of filler aggregates, it is possible to impregnate said supports with chemicals attracting ambient humidity, such as, in particular, CaCl ₂ , associated with an anionic wetting agent, not influencing the hydrophobicity of said supports, and, where appropriate, petroleum solvents, which may contain, in dilution, the long chain organic acid necessary for hydrophobing said supports, the percentage by weight said petroleum solvent (s) being between approximately 0.01 to 0.1% of the weight of said aggregates. The aforementioned chemicals, such as CaCl ₂ , deposit, by their constant hygroscopy, a film of water which is interposed, in juxtaposition, not physically wetting for the hydrophobic aggregates, thus forming a screen by slowing the formation of dust.

The wetting agent used in the context of the present invention is preferably of the C ₁₂ dodecyl-2-sulfate type, introduced either into the emulsions of hydrocarbon binders during their manufacture, or into the specific chemicals used to hydrophobize the supports, or still injected when the binders and supports are brought into contact. These wetting agents promote the desired adhesive rupture of the coating emulsion, applied to hydrophobic aggregates, this action remaining for said hydrophobic granules after drying.

In accordance with another characteristic of the invention, the supports, in particular the aggregates, are hydrophobic during their secondary or tertiary crushing, preferably in ballast pits or quarries, making it possible, due to their crushed, practically dry state, to limit, or even eliminate the use of products drying and create hydrophobic supports that can be stored in the open air, without the risk of waterlogging.

Petroleum solvents can advantageously be mixed with long-chain organic acids, which are solid at room temperature, with a view to their liquefaction without providing heat for cold coating. Said solvent, strongly adsorbed by the hydrophobic aggregates, constitutes, around them, a microscopic film and acts in the manner of a softening bond between the relatively hard bitumen provided by the emulsion and the support to be coated, while accelerating breaking.

In addition, the invention makes it possible, by integrating an emulsion manufacturing plant according to document FR-2 608 185 in a cold-coating plant, capable of transforming the bitumen on arrival at the refinery at the rate of its unloading in immediately usable emulsion, having a generalized application, to short-circuit the expensive operations of hot coating by appreciably reducing the investments and the pollution of the environment, by authorizing the implementation, in all cases, of '' a simple, compact and low-polluting cold coating station.

Thus, the method according to the invention dispenses with the coating binders - including the emulsions - from having to promote the adhesive and breaking properties of the supports to be coated. The cationic effect is therefore no longer required for a coating emulsion, nor is doping for non-emulsified binders.

It should be noted that the aggregates thus hydrophobic can be validly and adhesively coated with all the emulsions, cationic and anionic or amphoteric, sufficiently stable with respect to the fines contained in the mineral aggregates, while having a progressive and controllable rupture, this which is easy for anionic emulsions and remains difficult or even impossible for conventional cationic emulsions.

Subject to a hot coating, these aggregates, activated to preferentially attract hydrocarbons, can be used to raise the quality of the coated materials at the level obtained for the coating of the banks of the Arzwiller canal, in Lorraine, whose aggregates, before passing through the dryer drum, were treated with a solution of basic chromium salts and which, coated, were monitored, day after day, by the Regional Laboratory of Bridges and Roads of Strasbourg and constantly showed the maximum, ie 1, for the DURIEZ Immersion / Compression index.

As regards the universal cold coating proposed by the present invention, anionic emulsions, which are less expensive, easily fabricable and stabilizable as desired, will preferably be chosen, the adhesive rupture of which is started by the hydrophobic state of the aggregates.

An anionic emulsion thus stabilized, to the point of being capable of coating the fines, if they were taken apart, is necessarily capable of coating all the formulations practiced by hot coating.

The rupture induced by hydrophobicity, which can be modulated by any means with progressive effect, is always done adhesively. Thus, the bitumen (of negative electrical charge) that the rupture expels from the emulsion, is found in front of hydrophobic facets (with positive electrical charge) of which it becomes the first occupant.

We therefore preferentially coat with this emulsion, stabilizable at will, but also breakable at will, universally applicable to all granular formulations, including the most fillerized, if necessary pure or virgin, for recycling or more or less soiled.

With regard to obtaining hydrophobicity, it has been observed that the product which results from the reaction of basic salts of trivalent chromium or of metal salts of the type FeSO ₄ 7H ₂ O with fatty acids, gives the surfaces dry that it touches, a permanent hydrophobicity, immediately exploitable. This is also true for other organic acids, carbon chains long, containing more than 10 carbon atoms, an example of which are naphthenic acids.

To obtain this hydrophobicity under site conditions, in the presence of moisture, it is necessary to dry, before or after adding the specific chemicals or hydrophobicity vectors to the aggregates.

When carrying out work on site, aggregates are generally used, in the form of reserves, in the open air and the possibility of being able to use dry materials is very low.

The present invention also makes it possible to carry out a coating on wet materials without having to treat them by means of a drying drum.

In the case of cold coating in accordance with the invention, the hydrophobic effects of basic trivalent chromium salts, respectively metal salts, in combination with a fatty acid, are exploited by adding them simultaneously or successively to the aggregates to be hydrophobed, and by performing, if necessary, cold drying. The reaction between these hydrophobicity vectors (salts + fatty acids) takes place in situ, which leads to perfect hydrophobicity, especially for the fillerized granular compositions.

However, the most rational way of proceeding consists in treating dry materials for which the low water supply (approx. 0.3%) by the hydrophobicity vectors does not require drying. Cold drying, almost instantaneous, is necessary and possible for non-fillerized granulations.

Starting from wet aggregates, it has been found that drying can be obtained, without harming the hydrophobicity, by the addition of a product which fixes this humidity by hydration, such as for example quicklime CaO, after the reaction: CaO + H ₂ O = Ca (OH) ₂ . However, very slightly wet or dry hydrophobic aggregates are preferable.

This condition seems to be best met at the time of crushing, in ballastière or in quarry. Even if the rollers or blocks to be crushed are wet at the start, the moisture content found in the crushed aggregates of secondary or tertiary crushing is practically zero, which avoids having to carry out drying or limiting this last.

Choosing quicklime as a drying agent, to remove 18 kg of water, add 56 kg of quicklime, according to the formula:

CaO + H ₂ O = Ca (OH) ₂ .

The presence of Ca (OH) ₂ in hydrophobic aggregates, at the time of coating with the anionic emulsion, influences the rupture and this must be taken into account in the way of stabilizing this emulsion. However, prolonged storage of these hydrophobics, dried with quicklime, leads to calcium carbonate, without chemical action on the rupture of the coating emulsion. They constitute super-added fines, like besides lime Ca (OH) ₂ , which can be taken into account in the formulation of the skeleton of the products to be coated.

For a humidity of 0.3% for example, before adding the hydrophobicity vectors, 9.6 kg of quicklime per tonne of aggregates is needed, i.e. approximately 10 kg of industrial quicklime, which would be equivalent to a additional filling of approximately 1%. But by a rational organization one can arrange so that hydrophobicity is acquired without drying.

Thus, the ballast pits or the quarries, provided with the means necessary to obtain hydrophobicity, could deliver ready-made granular coating compositions, on command of the wrappers, which would see their coating operations simplified as much as possible. Ultimately, users who would buy the coating emulsion with hydrophobic aggregates, already conditioned, could make their mixes cold in their concrete mixers or mixers.

The contractor can hydrophobize his aggregates himself, by buying his aggregates "under the crushers" and by hydrophobing them at the arrival, without first storing them in the open air. Knowing that the drying drum will no longer intervene to disturb its granular compositions, it will arrange with its supplier to have all made the granular compositions of its mixes.

Thus, these hydrophobic products allow all the options and introduce great flexibility in the implementation of the cold bituminous coating technique. The direct cationic emulsions of the prior art, which must be adapted to each coating problem, are no longer necessary and can be replaced by a single anionic emulsion for any granular composition to be coated, having a universal coating power. , the cationic effect of adhesive rupture, acquired once and for all, having been transferred to the aggregates, which carry a positive electrical charge.

This flexibility is found in keeping the possibility of hydrophobic aggregates in stock, in the open; which gives the entrepreneur the opportunity to fill idle times by their forecast manufacturing.

As for the conclusion, generally too hasty, concerning possible nuisances due to chromium salts, it is recalled that these are exclusively trivalent chromium salts which, moreover, are made insoluble in the stages of the process according to l 'invention. It is, moreover, recalled on this subject that it is the same salts which have been used constantly for more than a century in the tanning of leathers. Now these chrome-tanned leathers surround us on all sides, in private and in public, where they undergo constant wear and tear of which we breathe the dust, entire lives, without damage. In addition, in accordance with the invention, protection is provided by the bituminous coating which eliminates the dust and prevents any aqueous dilution, in the same way as the tar tar residues are currently neutralized by the bitumen layer of the coating of recycling aggregates.

It is also recalled that the crushed or hydrophobic aggregates according to the invention can also constitute the supports for hot mixes, giving them an almost indestructible quality in the constant presence of water. Hydrophobic aggregates in fact withstand the high temperatures encountered in the drying drums of hot coating (temperatures above 200 ° C.), without losing their adhesive property. Thus, a maximum DURIEZ I / C index, equal to 1, is easily obtained and the cost of obtaining hydrophobicity is practically made up for by the fuel savings made on the hydrophobic aggregates which are treated by the drying drum without practically have brought water to drain.

The products obtained by means of the process according to the invention are, as indicated above, mainly constituted by supports rendered hydrophobic, in the form of pure or virgin aggregates, covered, where appropriate, with a hydrocarbon binder, bituminous type.

However, the supports may also be present, either in the form of unwashed aggregates, rendered suitable for coating by their hydrophobic treatment, or, advantageously from an economic point of view, in the form of recycled aggregates, coming from old road surfaces.

The invention can also find applications in other fields.

Indeed, the hydrophobicity obtained according to the invention is not exclusively intended for bituminous coating, but it is practicable on surfaces other than mineral surfaces, namely in particular woody surfaces.

Sawdust, for example, is likely to be hydrophobic, even more simply than mineral aggregates. Indeed, since sawdust generally contains more than the necessary quantity of fatty acids, it suffices to add only the chromium or iron salts to obtain their hydrophobicity. As they then strongly attract hydrocarbons, in all their forms (even paraffin oil), they can be used for the purification of water polluted by hydrocarbons.

Hydrophobic sawdust, not covered with bituminous binder, can therefore be proposed as depollutants for water contaminated by hydrocarbons or other oils, and be used in the fight against pollution by firefighters or protective forces similar civil, constituting even after storage in the open air and an additional commercial recovery.

The phenomenon is spectacular when we manage to ignite the hydrocarbons collected by sawdust made hydrophobic, floating on the water. The sawdust works like a wick, without burning itself, which can even be recovered to be used again, its hydrophobic qualities remaining intact.

This solution can be proposed in order to combat disasters caused by oil tankers at sea, by igniting hydrocarbons on the water, retained by sawdust or other hydrophobic materials lighter than water, such as expanded minerals for example.

The different application variants of the process according to the invention, described above, therefore solve in a global and practical manner the problems of bituminous coating in general and those of cold coating with emulsions in particular.

It is recalled that the anionic emulsion, respectively amphoteric, at the base of the process according to the invention, consists of the qualities of bitumens, used in hot coating, therefore not cut with solvents.

It is interesting, in this regard, to consult the publication of the French Ministry of Regional Planning, Equipment and Transport, under the title: "The bitumen emulsions" Special W, published in 1974. A current reissue born could not yet present a cationic emulsion whose performance could be compared with that of hot coating.

It is still still necessary, in the technique of cold coating with direct cationic emulsions, to carry out research on emulsifiers capable of solving the problems of the practice of construction sites. Too many factors force this choice, such as the quality of the bitumen to be emulsified, the mineralogical nature of the aggregates used and especially the nature and the degree of fillerization of the aggregates proposed for coating, (see document "Special W" above, pages 6 and 26). It suffices to read, on page 36 of said document "Special W", the method of adaptation of a cationic emulsion, requiring tedious research almost for each case of coating. Even if progress has been made since, a generalization of the cold coating as proposed in the context of the present invention, with the help of a single type of emulsion, is not yet in sight for coatings with cationic emulsion.

Consequently, there does not seem to exist, with reference to cationic emulsions, an emulsion for universal use.

On the other hand, as indicated above, the invention makes it possible to obtain an emulsion for universal use starting from an anionic emulsion which, by a roundabout path, or by making it cationic - which already places it further in the possibilities cationic emulsions of direct manufacture - either by abandoning its cationic transformation, by replacing it with an anionic emulsion stabilized at point, but which can be brought to an adhesive rupture - cationic so to speak - on hydrophobic aggregates, than reading the document " Special W "mentioned above could make believe technically impracticable.

Proof that obtaining the hydrophobicity according to the invention can be assimilated to a cationic action is provided by the marketing plates for basic trivalent chromium salts from the company Bayer, Leverkusen, which offers for sale these salts for tanning leathers, designating this tanning as being a cationic action. The reaction of basic trivalent chromium salts with a long chain organic acid is similar.

Another important application of the process according to the invention relates to the reuse of the bituminous carpet debris deposited.

The reduction in aggregates of this waste provides the recycling material and the users of these materials know that, at first glance, these emulsions do not wet them, because they are hydrophobic in nature due to the film of hydrocarbon binder which remains. , strongly glued, on these supports.

The latter constitute materials ready for adhesive coating with the anionic emulsion "superstabilised" or "overstabilized", with controlled rupture, according to the invention. As their particle size always needs to be corrected and adapted to the intended formulation, this can be achieved by adding aggregates, also hydrophobic, which are those obtained by the process according to the invention and which provide the effect cationic which the recycled aggregates take advantage of or quite simply by hydrophobing them in accordance with the invention.

All the granular combinations are possible and we will try to follow the current practice which consists in introducing a maximum of recycling products, which can exceed 80% by weight. This maximum does not imply any mechanical adaptation of the coating installation, which is not the case for recycling in hot coating.

Another important factor is the packaging and transportation of asphalt mixes, as well as their placement.

These problems are determined by the percentage of water that the asphalt contains at the outlet of the mixer and by the failure mode imposed. Controlling this rupture, in particular in the presence of fines from hot formulations, is difficult, if not impossible for direct cationic emulsions, but can easily be produced for the universal use emulsion according to the invention.

Thus, for the formulas: dense mixes - bituminous concretes for example, the addition of the emulsion according to the invention, without additional water, provides a complete coating in a force mixer, but with separate grains, difficult to compact, having the appearance of a hot mix and the same workability, with the advantage of being able to be transported by the same trucks as the hot mix and of being able to be put in place by the finishers of the hot mix hot. This form of cold coating would be ideal - really the parallel of hot coating - if the compaction difficulties could be overcome.

An additional water of the order of 5% by weight of the aggregates provides slightly pasty mixes, which are already more difficult to transport and handle. In this case, it is necessary to draw inspiration from the techniques of manufacture and installation of grouts and thin coatings, even those of cement concretes.

An additional 10% of water leads to the fluidity known for grouting. They are transportable at known distances for hot mix asphalt and withstand waiting times. Handling such a material requires mixing during transport, with the advantage of shortening and simplifying the current grouting process. It suffices to provide for the attachment of the distribution sled to the transporting trucks which take turns.

This technique allows rapid laying of thin bituminous mats, applying a comfortable fluidity, facilitating rapid compaction without loss of emulsion by flow.

It is recalled that all the thicknesses of belts practiced by hot coating are possible in the normal execution of the process described above. The breaking times are within the normal time limits for the duration of the roll used for hot coating. The rolling of cold-laid carpets should not spread beyond the time it takes for the emulsion to break, especially at low temperatures. These points in common between the hot coating and the cold coating produced in the context of the present invention are important.

In summary, the generalized bituminous coating process according to the present invention aims in particular at cold coating, by removing emulsions from the main constraints obliging contractors to adapt them to the multiple variables encountered on sites working with bituminous binders. It mainly replaces cationic emulsions which are hyper-sensitive to the mineral origin of aggregates, to their cleanliness, to their granular composition and their degree of filling, to the quality and quantity of the fine fines, etc.

Instead of adapting the emulsions to the infinite variability of the coating and site conditions, the method according to the invention goes further and adapts all the aggregates to all the forms of bituminous binders, including the emulsions.

To make possible this generalization of the bituminous coating, universally adhesive, the aggregates intended for a bituminous coating are treated with hydrophobic products, capable of transferring the specific effect of adhesive rupture of the cationic emulsions on the aggregates. It then suffices to bring any bituminous binder, with adequate fluidity, to the hydrophobic aggregates intended for coating and, as regards the emulsions, to break them up so that the bitumen is deposited with the guarantee of maximum adhesiveness. This effect is obtained by an emulsion in which the bitumen carries a negative electrical charge, the aggregates carrying a positive electrical charge.

The process for obtaining hydrophobicity according to the invention does not make a distinction between acid and basic or siliceous and calcareous aggregates and is not influenced by the quality or the quantity of fines present. It also does not use heating and drying. These operations - if necessary - are also carried out cold.

All the bituminous binders, brought into contact with the hydrophobic surfaces, adhere there adhesively, so that these coated materials, placed under water and subjected to a prolonged boiling, do not lose their coating. The DURIEZ I / C indices reach or tend towards their maximum value, namely 1.

Thus freed from the worries of starting the rupture of the emulsions and the adhesive bonding of the binders on their supports, it is advisable, for the coatings with the emulsions, to control the duration of this rupture and to adapt it to the circumstances encountered on construction sites and coating plants. This adaptation must be done with a "superstabilized" emulsion, capable of wetting all granular formulations, before breaking.

Knowing that cationic emulsions of direct manufacture cannot meet all these criteria at the same time (see on this subject the document "Special W"), use is made of an anionic emulsion capable of the required stability and the rupture of which is initiated by the hydrophobicity and the positive charge of the aggregates.

The stability of the anionic emulsion can be graduated by a variable alkali rate. By using proteins as stabilizers, almost all chemicals can enter such an amphoteric emulsion without destroying it, which can exist in any P _H.

Among these chemicals there are some which, in contact with the aggregates, develop a tendency to further rupture, reinforcing that induced by the hydrophobic aggregates.

This faculty to influence the rupture belongs to many substances among which are distinguished, by their effectiveness and their specificity, for example, magnesium sulphate MgSO ₄ , sodium sulphite Na ₂ SO ₃ and wetting agent C ₁₂ Dodecyl-2 -sulfate.

The effect of MgSO ₄ can be explained by its ability to precipitate the anionic emulsifier - generally a naphthenate or the salt of a fatty acid - forming an additional adhesive. The "emulsion" state is then no longer maintained except by proteins, but is maintained at all P _H.

The effect of the wetting agent will be explained later in the description.

The effect of sulfite can be shown by a simple anionic emulsion to which Na ₂ SO ₃ , without proteins, is added. The failure on non-hydrophobic aggregates is spectacular, but not adhesive. This breaking effect which persists for an amphoteric emulsion is corrected by the adhesive effect of hydrophobic aggregates.

The two effects would be cumulated in MgSO ₃ if it existed in commerce. Obtained by the reaction MgSO ₄ + Na ₂ SO ₃ = MgSO ₃ + Na ₂ SO ₄ , put in imbalance, sometimes by an excess of MgSO ₄ , sometimes by an excess of Na ₂ SO ₃ , it makes possible a precise control of the rupture.

Thus obtaining the hydrophobicity of the aggregates raises heavy mortgages which weigh on the emulsions intended for the cold bituminous coating.

Indeed, instead of having to provide the means of adhesive rupture on the non-hydrophobic aggregates and having to distinguish between the origin and the granular composition, the coating emulsion is freed from these functions and ensures only failure and stability control.

The acquisition by these emulsions of these degrees of freedom has significant technical and economic consequences which go beyond the framework of the field of cold coating.

The favorable effects can already start in the quarry or in a ballastière, as described above.

The supply by producers of aggregates of hydrophobic materials is aimed at both hot-mixers and cold-mix manufacturers and allows open storage, without these hydrophobic aggregates becoming wet or even wet.

These results are possible by the fact that the acquired hydrophobicity places all the mineral aggregates, whatever their provenance, on an equal footing with any form of bituminous binder.

As regards the binder in the form of an emulsion, it can be produced for universal use, since the hydrophobic aggregates all react, in spite of their different mineralogical origins, in an equal manner before an emulsion and require, for equal granularity, the same dose of binder.

The choice of the type of emulsion which must suit all the granulations, open or closed, is therefore important. It has been found that the anionic emulsion, which can be stabilized at will, has the greatest flexibility of adaptation.

Unlike the cationic emulsion of direct manufacture, its degree of stability can be modulated in a precise manner and within wide limits, by its level of alkalinity, possibly associated with a low level of proteins or other known stabilizers.

The use of a high level of alkalis, without resorting to proteins, has a marked influence on the rupture which becomes more incisive, which makes it possible to manufacture grouts with ultra-rapid rupture. If non-cationized proteins are used, these would therefore only serve to modulate the stability of the emulsion, on the rupture of which one can still have an influence by accelerators of the MgSO ₄ and Na ₂ SO type. ₃ , already mentioned above, to which are added petroleum solvents which serve at the same time to dilute the organic acids, capable of serving as hydrophobic vectors, those which the solid state does not allow to introduce into the aggregates, such as stearin or excessively pasty naphthenic acids, while olein for example is fluid at the temperature for obtaining hydrophobicity.

Regarding the manufacturing of the coating emulsion, it is no longer as imperative to add the proteins to an emulsion cooled below 70 ° C., as provided for in the design of the emulsion plant. of document FR-2 608 185. In the context of the invention, the addition of the proteins can be carried out at the same time as emulsifying water, which initiates low hydrolysis, producing peptides with lower molecular weights, but which are just as capable of ensuring the desired stability for the coating emulsion.

As for the preparation of a mix that can be stored for a few days for partial use and the filling of excavations, it can be obtained by adding, on a mix with separate grains, which results from coating with a emulsion based on a hard bitumen, a solvent, at a rate of approximately 0.2% of the weight of the mix.

The problem of dust in hot coating could have become that of cold coating using hydrophobic aggregates.

Indeed, these aggregates repel humidity permanently and the fines, always dry, can flutter according to the air currents. Mandatory handling of these materials would therefore raise this dust and pollute the site, which must be prevented at the source.

The ideal drying agent for removing moisture would be a chemical which initially attracts ambient humidity, which amounts to drying out, but which, at the end of the reaction, remains humidifying, and thus promotes a juxtaposition of rising moisture on hydrophobic aggregates, slowing the flight of dust.

Knowing that the hydrophobicity obtained by separate applications of a basic chromium salt, respectively of a metal salt, in particular of iron, and of a fatty acid is acquired as soon as these vectors, well homogenized in the mass of the aggregates, have past - if only for a moment - by a state of dryness, it was found that calcium chloride CaCl _{2 made it} possible to obtain this result.

It is good for this purpose to associate it with an anionic wetting agent of type C ₁₂ Dodecyl-2-sulfate, for O, 2% of CaCl ₂ and 0.02% of wetting agent relative to the weight of the aggregates, knowing that the excesses in the use of these products do not compromise the obtaining of hydrophobicity. The use of wetting agents of the C ₁₂ Dodecyl-2-Sulfate type in the stages of the invention results in a variant of the process, in that, even when used alone, it acts on the rupture, without the aid of chemicals indicated above, products which can however be associated with it to obtain said action.

The additional advantage consists in that, without drying, the breaking effect appears more clearly by adding this wetting agent in the undried aggregates and homogenized with the vectors of hydrophobicity.

The wetting agent can be provided by the solution of chromium salts of iron respectively, defined above, in which it is dissolved in an amount of 1 to 2.5% by weight of said solution or by the emulsion, in which it is dissolved. at a rate of 0.04 to 0.1% of the weight of the solution, or be added to the aggregates which rotate in a mixer.

Other minor problems arise during the compaction of the installed mats. Where in hot coating the compaction is done by rolling during the cooling of the asphalt put in place, in cold coating the maximum possible compactibility is almost immediately acquired by the coated aggregates which bathe in water, present in abundance and which is better lubricant than the hot binder, present in the quantity just necessary.

As long as the breaking of the emulsion is not complete, the compact placement of the aggregates is practically ensured by this excess of water and the rolling is secondary.

When the rupture is complete, the bitumen spherules touch each other as well as the facets of the aggregates, without yet forming a compact mass. Given the hardness of the bitumen at the base of the coating emulsion and the effectiveness of the adhesion of this bitumen to these facets, the carpet offers, from this moment, a resistance to compaction all the stronger as the bitumen is harder and the rupture is more advanced. Heavy rolling should then be avoided and time and traffic will complete compaction. The small dose of solvent possibly introduced into the aggregates, plays here a very effective role of connection and activation of the rupture.

It has also been observed, in particular during a rapid break, that the considerable strengthening of the carpets, under the effect of the break of the emulsion, is not only the result of the sizing, but is preceded by a mass gain, due to a contraction phenomenon, caused by the rupture which tightens the contacts. Too heavy and too much rolling could dislocate this first firming and would be a drawback. The best compaction is then the circulation that this firming is able to support quickly.

It is indicated by way of examples, a formula for manufacturing a coating emulsion, a method of obtaining hydrophobicity and a cold bituminous coating process with the abovementioned emulsion.

The emulsion with universal coating capacity is preferably obtained in the emulsion plant of our design and described in documents FR-2 608 185, FR-2 608 645 and FR-2 612 214.

This plant is mobile and can follow construction sites and integrate into a post or cold coating plant. The bitumen is dosed with the precise devices of hot coating. It arrives, acidified in a refinery, with an acid number between 1.8 and 2.5 mg KOH / g and can be supplied without increasing its price. Its calorie potential is used to heat the emulsifying soda water which contains for example 0.2 to 0.5% by weight of NaOH, the emulsifying effect being obtained from 0.15% by weight of NaOH.

Under the effect of the movement of the centrifugal pump placed in the tank of the said plant and especially by the saponification reaction between the acids incorporated or naturally contained in the hot bitumen, a mother anionic emulsion is formed spontaneously, without the action of a colloid mill, provided that the limit temperatures given by the practical formula: bitumen temperature + water temperature 220 ° C, are respected.

With reference to the drawings accompanying document FR-2 608 185, this emulsion is discharged into the first cooling (and water heating) tank by a centrifugal pump. After passing the other two cooling tanks 2 and 3, the emulsion is either discharged onto the aggregates, dosed accordingly, or put on hold in tanks. The protein flour level is of the order of 0.8% relative to the weight of the emulsion for ambient temperatures of 2 ° C to 15 ° C and can be increased to 1.2% for summer temperatures, when '' it is a question of transforming an anionic emulsion into cationic emulsion.

These percentages are valid for the vegetable proteins represented by the meal of oilseed meal. For their sterilization 0.1 to 0.3% of paraformaldehyde are necessary, whereas for ultra-fast grouting, the protein level can be reduced to 0.4% for example and the level of NaOH raised to the maximum tolerated by the anionic mother emulsion.

Thus, by way of example, to 450 kg of water at 40 to 50 ° C. is added, containing 1.35 kg of NaOH, ie 0.3%, 550 kg of acidified bitumen, and having a temperature of 160 °. C at 170 ° C. These operations are carried out in an emulsion factory under electronic control.

To this still hot emulsion are added 8 kg of protein flours for example, having a protein level of between 45 and 50% and 100 g to 200 g of paraformaldehyde, always under electronic control, if the emulsion is made in the factory mentioned above, with a view to converting it into a cationic or amphoteric emulsion.

With regard to obtaining hydrophobicity, it should be noted that the levels of the hydrophobicity vectors are a function of the surface of the aggregates. For the present example, dry aggregates from a specific "rollobar" grinding are chosen, which reduces unsold crushed material without fines and produces aggregates containing more than 17 % of fines, consequently having an exceptionally large surface area to be hydrophobed.

To 1000 kg of these dry aggregates is added, in a force mixer, 1 kg of basic trivalent chromium sulphate commercial, as it is used by tanneries, after having diluted it in 3 liters of water. For the iron salts of the FeSO ₄ 7H ₂ O type, 1.2 kg dissolved in 3 liters of water are used.

At the same time, 0.4 to 0.8 kg of commercial olein or naphthenic acid diluted in approximately their weight of a petroleum solvent are added.

After homogenization, the hydrophobicity is acquired and the aggregates could be stored in the open, without them becoming waterlogged. They could also be coated with the emulsion described above, in the same homogenization mixer for the hydrophobic vectors. For a primary humidity of 0.3% by weight, for example, it should be dried with 10 kg of CaO or 3 kg of CaCl ₂ or 3 kg of anhydrous MgSO ₄ . To be sure that the aggregates, almost dry at the start, have gone through a moment of frank dryness and so that they are protected against theft of dust, it is preferable to add 1 to 5 kg of CaCl ₂ .

To the 1000 kg of hydrophobic aggregates described above, rotating in a kneader, are added, for the purpose of coating, 0 to 125 liters of water and 125 kg of the 55% emulsion whose manufacture has been described and it is checked that the breakage and the maneuverability correspond well to the needs of the sites to be served.

For a minimum acceleration of the rupture, fitting with a universal coating emulsion, one can add a certain quantity of MgSO ₄ 7H ₂ O in the basic chromium sulphate solution which is capable of absorbing 20% of it. its weight at 12 ° C, with no sign of insolubility deposit.

Thus in the previous example, by adding 4.8 kg of this solution, which amounts to adding 0.8 kg of MgSO ₄ 7H ₂ O to the 125 kg of emulsion, about 0.6% of anhydrous MgSO _{4 is added.} based on the weight of the bitumen.

Surprisingly, the obtaining of the hydrophobicity is not disturbed and the heap of aggregates thus hydrophobic protects the MgSO ₄ - as it would protect the CaCl ₂ , which however continuously attracts moisture from the ambient air and seems, at least apparently, to wet hydrophobic products.

The latter are therefore capable of keeping water-soluble chemicals in juxtaposition and of keeping them in reserve for future action.

Hydrophobic aggregates which appear to be wetted by the constant attraction of moisture by CaCl ₂ are only apparently so and continue to refuse any additional water added.

At the time of coating with the emulsion, these products, protected in the middle of the hydrophobic aggregates, become active and MgSO ₄ for example, can play its role of rupture accelerator. The accelerator rates may vary depending on the design of the coating emulsion and its balancing.

This approach could extend to other products which may play a useful role in the coating, provided that they do not prevent the obtaining of hydrophobicity. Among these useful products, mention may be made of solvents.

Thus, the present invention allows the realization of a generalized coating process which can be implemented hot or cold.

Indeed, instead of forcing the bituminous binders and their emulsions to have to provide the adhesive coating capacity to their supports themselves, while creating the good conditions for their maneuverability, the process according to the invention frees these binders of these subjugations which are often difficult to carry out, by adapting in a definitive and unequivocal manner all the supports to all the binders and forms of binders which no longer have to be doped for non-emulsified, or made cationic as regards emulsions.

To do this, the supports to be coated are hydrophobic, that is to say made capable of repelling water and humidity and of remaining dry. under bad weather, which makes it possible to store them in the open air in a form which no longer brings water to evaporate in the drying drums, thereby reducing the consumption of fuel and, consequently, the pollution of the atmosphere .

For this, it is sufficient to dry the specific chemicals on their supports only once so that the hydrophobicity appears and remains acquired. This drying will no longer be done by heating, but cold, using suitable inexpensive and water-hungry chemicals, thus avoiding drying by tumble dryer or microwave oven and allowing immediate coating or term of said supports.

This hydrophobicity puts the supports to be coated - without distinction of provenance or granular conditioning - in equal behavior before each binder or form of binder, taken separately. It is sufficient to put this binder each time in a condition of adequate fluidity and, as regards the emulsions, to stabilize them to the point and to route them towards a progressive rupture.

Each binder or form of binder is suitable for each hydrophobic support and the emulsion remains equal to itself, without having to adapt it to the aggregates by changes of emulsifiers.

By the use of certain wetting agents, the aggregates, homogenized with the hydrophobic vectors, can be validly and adhesively coated with the stabilized emulsion according to the invention, without having to dry them beforehand.

According to an alternative embodiment of the invention, the process described above can also consist, after separate or simultaneous addition of the two specific chemicals on the supports to be hydrophobed, to carry out a very rapid drying of the latter by means of a mixture of cement and lime, homogeneously integrated into the mass of supports and aggregates subjected to the hydrophobic treatment, said supports thus also acquiring a positive electrical charge.

Indeed, it was possible to accelerate the hydrophobic act by exploiting the exceptional characteristics specific to mixtures of cements and lime, namely, their strong hydrating power, allowing them to quickly absorb the moisture with which they are put. in touch.

If a mixture of molten cement and lime is absolutely prohibited and contraindicated in the cement concrete technique, it does not disturb in bituminous concrete where the binding and stiffening value of the cement and lime, but where the fines created by these mixtures, in addition to those already present in aggregates, stabilize bituminous concretes. This additional filler should therefore be taken into account when formulating cold mixes.

It has been found that a mixture of, for example, about 80% molten cement and about 20% lime, by weight, greatly accelerates the process to reach hydrophobicity, which even before all of the l he moisture contained in the aggregates is transformed into hydrated water, causes this remaining water to float on the aggregates, without physically wetting them, and repels any other added water.

This property thus immediately prevents fines from forming clouds of dust, a phenomenon which is combated as described above by other specific means.

The advantage of the early onset of hydrophobicity therefore goes hand in hand with a substantial saving in hydrophobic agents, namely the chromium or iron salts and the long chain organic acid described above.

Cement-lime mixtures bring other advantages which consist, in particular, in fixing the acid salt - preferably iron sulphate or chromium sulphate - on the aggregates or aggregates before the alkali stabilizing the emulsion comes combine with the lime provided by the cement-lime mixture. By choosing, as alkali, sodium carbonate for example, this lime, with also using the CO ₂ from the air, turns into limestone CaCO ₃ which is the ideal filler for bituminous mixes, which must also be provided in accordance with the prescriptions of certain countries such as, for example, the Netherlands.

It suffices that the fatty acid or similar pair (olein for example) / metallic acid (iron sulfate or chromium sulfate for example) is dried - if only for a moment - on the supports or aggregates for the hydrophobicity appear and be acquired once and for all. This trend is strongly accentuated with the use of a cement-lime mixture.

It is indeed technically desirable that this drying act is not a heating (drum-drier) or even less a slow drying under shelter at room temperature, but that it is accomplished at the same rhythm of the course of the coating. when cold on aggregates thus acquiring a positive charge.

It has been found that hydrophobicity is acquired by rates of cement-lime mixtures which are lower than their hydration capacity. Thus it is possible, in the current state of research of the applicants, to hydrophobate aggregates containing more than twice the weight in water than that of the cement-lime mixture used.

These are supports or aggregates with a positive electrical charge whose hydrophobicity means that they preferably attract bituminous binders, rather than water.

Under these conditions, coating with conventional bitumens and cut-backs is facilitated and does not present any particular difficulties, it being noted that these hydrophobic supports or aggregates, possibly stored in the open air and exposed to the weather, do not become waterlogged , which therefore no longer needs to be evaporated by means of drum-dryers.

As for the cold coating, the anionic emulsion, of which the bitumen is negatively charged, is ideal. It suffices that it has sufficient stability to envelop these hydrophobic aggregates before breaking, as described above.

The opposite signs of the charges of the aggregates, on the one hand, and of the bitumen globules of the anionic emulsion, on the other hand, cause the same adhesive rupture as that which is obtained with cationic emulsions, positively charged, in reaction. with negatively charged silicas.

Claims (17)

1. Coating process, intended for adhesively fixing plastic and elastic binders either in fluidised form owing to heat or solvents or in emulsified form to substrates, in particular of the granulates type, characterised in that it mainly involves pretreating the substrates to be coated to render them hydrophobic and carriers of a positive electric charge under the influence of two specific chemical products namely, on the one hand, a metallic acid salt and, on the other hand, a long chain organic acid, so as to render their behaviour uniform with respect to all the hot or cold binders and in all their forms, to enable them to attract these binders, preferably in water, and to place said binders in contact with these hydrophobic substrates for the adhesive and homogeneous deposition thereof on said substrates.
2. Coating process according to claim 1, characterised in that the hydrophobicity of the substrates to be coated is achieved by the action of two specific chemical products, namely iron sulphate FeSO₄7H₂O and a fatty or naphthenic acid.
3. Coating process according to claim 2, characterised in that it involves, after separate addition of the two specific chemical products to the substrates to be hydrophobised, carrying out rapid cold drying thereof so that said substrates acquire a positive electric charge.
4. Coating process according to claim 2, characterised in that it involves, after separate addition of the two specific chemical products to the substrates to be hydrophobised, carrying out very rapid drying thereof by means of a mixture of cements and lime so that said substrates acquire a positive electric charge.
5. Coating process according to claim 4, characterised in that the cement used in the mixture of cement and lime consists of fused cement.
6. Coating process according to any one of claims 1 to 5, characterised in that the binders used are hydrocarbon-containing binders in the form of distillation residues of crude oils cut or uncut with solvents and fluidised, if necessary, these binders being identical to those used for conventional hot coating or for cold coating with cutback bitumens.
7. Coating process according to claim 6, characterised in that the hydrocarbon-containing binders are used in the form of emulsions of which the bitumen globules carry a negative electric charge, which break in contact with the hydrophobised substrates while depositing the binder there in a homogeneous and adhesive manner more or less rapidly depending on the degree of stability of said emulsions.
8. Coating process according to claim 7, characterised in that the stability of the emulsions is monitored by means of the contents of alkalis present therein, alone or in combination with proteins or other stabilising agents or again breakage accelerating agents such as, for example, MgSO₄, Na₂SO₃ or petroleum solvents.
9. Coating process according to claim 8, characterised in that the breakage accelerators can be either introduced into the coating emulsion together with the protein flour or mixed in the form of solutions with the acid salt of iron sulphate or with the long chain organic acid, in particular a fatty acid, used to hydrophobise the substrates to be coated.
10. Coating process according to any one of claims 8 and 9, characterised in that it involves preferably mixing the petroleum solvents with the long chain organic acids which are solid at ambient temperature in order to liquefy them without the contribution of heat for a cold coating.
11. Coating process according to claim 2, characterised in that, in order to prevent the fines possibly present from fluttering around during handling of the substrates to be coated in the form of filler-containing granulates, it involves impregnating said substrates with chemical products which have a drying action but continue to attract the ambient moisture such as, in particular, CaCl₂ optionally combined with an anionic wetting agent which does not affect the hydrophobicity of said substrates and, if necessary, petroleum solvents which can contain, in diluted form, the long chain organic acid necessary to hyrodrophobise said substrates.
12. Coating process according to claim 11, characterised in that the wetting agent is preferably of the C₁₂ dodecyl-2-sulphate type introduced either into the emulsions of hydrocarbon-containing binders during the manufacture thereof or into the specific chemical products used to hydrophobise the substrates or again injected when the binders are brought into contact with the substrates.
13. Coating process according to any one of claims 1 to 12, characterised in that it involves hydrophobising the substrates, in particular the granulates, during the secondary or tertiary crushing thereof, preferably in the ballast pits or quarries allowing the use of drying products to be limited or even eliminated owing to their virtually dry crushed state and allowing hydrophobised substrates which can be stored in the open air and do not run the risk of becoming water-logged to be produced.
14. Products obtained by the coating process according to any one of claims 1 to 13, characterised in that they consist mainly of substrates which are rendered hydrophobic, in the form of virgin or pure granulates covered with a hydrocarbon-containing binder of the bituminous type.
15. Products obtained by the coating process according to any one of claims 1 to 13, characterised in that the substrates have the form of contaminated granulates which are made suitable for coating by their hydrophobic treatment.
16. Products obtained by the coating process according to any one of claims 1 to 13, characterised in that the substrates have the form of recycled granulates originating from former bituminous coverings.
17. Products composed of substrates having the form of wood shavings or expanded minerals which are lighter than water and are rendered hydrophobic by the action of two specific chemical products by the process according to any one of claims 1 to 6, 12 and 13 and not covered with binder, these substrates being able to be stored in the open air without losing their hydrophobicity for the anti-pollution application for contamination with hydrocarbons.